Accompanied by intelligence officials from their countries, they boarded planes to go home.

Ms Urru arrived in Rome late on Thursday where she was met at a military airport by family members and the Prime Minister, Mario Monti.

She said she was well and thanked those who had worked to secure her freedom.

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''I was treated well, even if I was frightened several times,'' she said on arrival, adding that she hoped to return to resume her work in Africa.

The previously unknown group - a self-proclaimed offshoot of al-Qaeda in the Islamic Maghreb - claimed responsibility for kidnapping the aid workers in October and on Wednesday announced their release.

The Movement for Oneness and Jihad in West Africa holds Gao, while Ansar Dine has exerted its control in Timbuktu, whipping unmarried couples, smokers and drinkers and destroying ancient world heritage shrines it considers idolatrous.

Both Islamist groups have stated ties to al-Qaeda in the Islamic Maghreb and other jihadist groups on the continent, raising fears that the vast region could become a safe haven for extremist groups.